Removal of waxy sludges from pipelines and oil wells



United States Patent Ofice 2,753,939 Patented July 10, 1956 REMUVAL FWAXY SLUDGES FROM PIPELINES AND ()IL WELLS Clayton A. Carpenter, LaHabra, and Paul W. Fischer, Whittier, Califi, assignors to Union OilCompany of California, Los Angeles, (Zalili, a corporation of CaliforniaNo Drawing. Application March 15, 1954, Serial No. 416,444

" 14'Claims. (Cl. 166-41) This invention relates to the removal ofparaffin and waxy sludges from oil wells and from petroleum-carryingpipelines, and in particular concerns new and improved compositions ofmatter and methods for accomplishing this result.

In many of the oil fields in the United States, particul-arly in thosewhich produce relatively heavy waxy crudes, production is limited as aresult of paratfin and waxy sludges depositing from the crude andplugging. up the well tubing and pump as well as the oil-producingformation itself. In many instances the flow of oil from a well has beencompletely arrested as a result of such deposition. A similar depositionof wax and sludge occurs in pipelines which form crude oil gathering andtransportation systems, and results in increased pumping costs and/orfrequent disassembly and cleanout of the pipeline system.

For the most part, the many attempts to obviate these difiiculties havetaken the form of heating the crude oil to melt the waxes and sludge andpromote their solution in the crude, or employing a solvent to dissolvethese materials, or both. The technique of hot-oiling a well, whereby arelatively light petroleum fraction is heated and forced into the wellunder pressure to dissolve waxy sludges deposited therein, has long beenknown but the relative inefiectiveness of this technique has equallylong been recognized and has led to numerous proposals to employ asolvent other than petroleum distillates. Insofar as is known, however,none of such solvents has proved commercially satisfactory.

It is accordingly an object of the present invention to provide animproved method for removing parafiin, waxy sludges andthe like from oilwells and petroleum pipelines.

Another object is to provide a method whereby paralfin, waxy sludges andlike deposits are removed from oil wells and petroleum pipelines bymeans of a solvent.

A further object is to provide new and improved solvents for theparaflin, waxy sludges and the like which are deposited from crude oils.

Other and related objects will be apparent from the following detaileddescription of the invention, and various advantages not specificallyreferred to herein will be apparent to those skilled in the art uponemployment of the invention in practice.

We have now found that the above objects and attendant advantages may berealized through the use of a particular type of solvent mixture whichhas high solvent power for parafiin, waxy sludges and the like and issufliciently high boiling that it can be used at relatively hightemperatures. More particularly, we have found that parafiin, waxysludges and the like which are deposited from even very heavy crudes canreadily be removed from oil wells, petroleum pipelines and the like bycontacting the materials to be removed with a mixed solvent comprisingan aromatic hydrocarbon, an: etheralcohol, and a dialkyl ether, all ofsaid components beingliquids having boiling points substantially abovethat of water. By reason of their high-boiling points, such solventmixtures are admirably adapted to being used in combination with heat,particularly in treating wells as is hereinafter more fully explained.

The aromatic hydrocarbon component of the present solvent mixtures maybe any normally liquid aromatic hydrocarbon which has a boiling pointabove about 100 C., e. 'g., toluene, xylene, ethylbenzene, cumene,mesitylene, propylbenzene, etc. Mixed aromatic hydrocarbons may also beemployed, e. g., petroleum hydrocarbon reformate fractions, keroseneextracts, and mixed aromatics derived from coal tar. Toluene is usuallypreferred.

The ether-alcohol component may be any normally liquid aliphatic etherof an aliphatic polybasic alcohol, which contains at least one freehydroxyl group and has a boiling point above about 100 C. Suitableetheralcohols of this type include the mono-methyl, -ethyl, -propyl, and-butyl ethers of ethylene glycol and diethylene glycol, the monoanddi-methyl, -ethyl, -propyl, -butyl ethers of glycerol, the mono-methyland -ethyl ethers of butanediol, etc. Ether-alcohols of this type containing less than about 12 carbon atoms are preferred.

The ether component may be any normally liquid dialkyl ether having aboiling point above about 100" 0., e. g. di-n-butyl ether, di-n-amylether, di-isoamyl ether, di-octyl ether, .propyl-amyl ether, ethyl-hexylether, methyl-lauryl ether, butyl-octyl ether, etc. Ethers of this typecontaining less than about 12 carbon atoms are preferred.

The proportions in which the foregoing components are combined toprepare the new solvents are approximately as follows:

Percent by volume Aromatic hydrocarbon -1--- 50-85 Aliphaticether-alcohol 10-40 Dialkyl ether a 5-30 A particularly preferredsolvent of the present class comprises between about 60 and about percent by volume of toluene, between about 15 and about 30 per cent byvolume of the monobutyl ether of ethylene glycol (Butyl Cellosolve), andbetween about 5 and about 15 per cent by volume of di-butyl ether.

The use of the above-described solvent mixtures for the removal ofparafiin, waxy sludges and the like may take a variety of forms. Usuallythese solvents are most effective when applied in conjunction wtihheating, but in some instances they may be used cold. In treatingpipelines and the like the solvent is merely pumped through the line,preferably under moderate pressure and in a heated condition.Particularly efiective results are s'ecured when the direction of flowis reversed periodically, whereby there is achieved a mechanical washingeflt'ect which supplements the solvent action. The same general mode ofoperation may be employed in cleaning out tanks, pumps, refineryequipment and the like in which waxy sludges accumulate.

In treating wells to increase the production thereof, various techniquesmay be employed ranging from simple application of the cold solvent tothe tubing, pump and other pieces of well equipment to more complicatedprocedures directed to treating the oil-producing formation with thesolvent at points considerably removed from the Well bore. The followingexamples will illustrate several ways in which the principle of theinvention has been applied to treating wells but are not to be construedas limiting the same.

Example I A certain well in the Cut Bank, Montana, field was producing38.4 API gravity crude at an average rate of 3 about 6.0 bbls./day. Thiswell was taken out of production and 159 gallons of a 60:30:10 parts byvolume mixture of toluene, Butyl Cellosolve and di-butyl ether wasintroduced into the well annulus. Natural gas was then forced into thewell until aback-pressure of about 360 p. s. i. was attained. Thenatural formation pressure was about 260-280 p. s. i., so that thesolvent was forced into the formation under a differential pressure ofabout 80100 p. s. i. The well was maintained under back-pressure forabout 24 hours, after which the pressure Was released and the well wasplaced in production. No appreciable increase in the average dailyproduction from the well which could be attributed to the solventtreatment was immediately observed. After about two months operation,however, the production increased by about 18 per cent. This increasewas not observed in adjacent wells which had not been treated with thesolvent.

Example 11 An electrically heated well in the Cut Bank field wasproducing at an average rate of about 6 bbls./day. Approximately 159gallons of the solvent employed in Example I were introduced into thewell annulus, and heating was continued for about 4 hours with the wellshut in. The well was then pressured to about 320 p. s. i. with naturalgas, and heating was continued for about 16 hours while maintaining suchpressure on the well. The pressure was then released and the well wasplaced in production. The average daily rate of production immediatelyrose by about 50 per cent. At the end of a three-month test period thewell was still producing at the increased rate.

A particularly preferred embodiment of the invention involves the use ofthe present class of solvents in conjunction with a hot-oilingtreatment. As conventionally employed, such treatment in generalcomprises in troducing a heated petroleum hydrocarbon, e. g., kerosene,diesel fuel, gas oil, light crude, etc., into the well and applyingpressure to force thehot hydrocarbon deep into the pores and intersticesof the oil-producing formation. Since the object of such treatment is topenetrate the formation as deeply as possible with hydrocarbon as hot aspossible, it is essential that the hot hydrocarbon be forced into theformation as rapidly as possible. In many wells, however, the formationis so heavily clogged with waxy deposits, and consequently the rate atwhich the hot hydrocarbon can be forced into the formation is so slow,that the hydrocarbon becomes cold before it penetrates into theformation to any appreciable extent. We have found, however, that if theWell is treated with the solvent mixtures provided by the presentinvention prior to hot-oiling, the rate at which the hot hydrocarbon canbe forced into the formation can in a great many instances be greatlyincreased. Consequently, the hydrocarbon penetrates deeply into theformation without undue cooling, and greatly improved results areobtained from the hot-oiling treatment. The following exampleillustrates one way in which the principle of the present invention hasbeen applied to improve greatly the results obtained from hot-oiling.

Example 111 A certain well in the Cut Bank field was brought in in 1936at an average production of 58 bbls./ day. Over the following yearsproduction declined gradually until, in 1951, it was down to 4bbls./day. In 1951 an electrical heater was installed in the well,whereupon production rose to about 12 bbls./day. Over the next two yearsproduction under the influence of heat gradually declined to about 6bbls./day. The heater was then removed, whereupon production dropped to5.6 bbls./ day over a l-month period. At this time, a tubing packer wasinserted in the well just above the formation, and 159 gallons of a cold60:30:10 mixture of toluene, "Butyl Cellosolve and dibutyl ether wasintroduced into the tubing. The well was pressured up to about 350 p. s,i. and allowed to stand for 3 days, after which time 200 bbls. of hot(300 F.) diesel fuel was introduced into the well. The tubing was pulledand the packer removed and a pump installed, and the well was placed inproduction one day after the injection of the diesel fuel. During thefirst week thereafter, the average production was about 34 bbls./day.Within 10 days, production fell to 20 bbls./day. The average productionfor the next 3 months was 17 bbls./day, and the well continued toproduce at about this rate except for temporary declines duringextremely cold weather. The overall increase in production secured bythe treatment was over 880 bbls. of oil for the 3 months immediatelyfollowing the treatment; The excellent results secured by the treatmentare believed to be due to the fact that the solvent mixture dissolvedand/or dispersed heavy waxy deposits in the formation in the immediatevicinity of the bore hole, thereby permitting the hot diesel fuel topenetrate deep into the formation within a relatively short period oftime so that a minimum amount of heat was lost from the oil before ithad penetrated the formation to any great extent. theory of operation issubstantiated by the fact that no difficulty was experienced ininjecting the hot oil into the formation at a relatively high rate.However, it should be understood that the invention is not limited byany theory of operation expressed herein.

-As will be apparent to those skilled in the art, the principle of theinvention may be applied in various ways and in combination with varioustechniques to effect the removal of paraffin, waxy sludges and the likedeposited from crude oil or petroleum distillates and residua in a widevariety of inaccessible places. In its broadest aspects, the inventionconsists in the herein defined solvent mixtures comprising aromatichydrocarbons, aliphatic ether-alcohols, and dialkyl ethers, and themethod of removing paraffin, waxy sludges and similar deposits frompipelines, oil'wells and the like which comprises contacting suchdeposits with said' solvent mixtures to effect their solution and/ ordispersion therein.

Other modes of applying the principle of our invention may be employedinstead of those explained, change being made as regards the materialsor methods disclosed herein, provided the steps or compositions setforth in any of the following claims, or the equivalent of'such steps orcompositions, be employed or obtained.

We, therefore, particularly point out and distinctly claim as ourinventionz l. A solvent for paratfin, waxy sludges and the like ofpetroleum origin comprising between about 50 and about per cent byvolume of a normally liquid aromatic hydrocarbon, between about 10 andabout 40 per cent by volume of a normally liquid aliphatic ether-alcoholcontaining at least one free hydroxyl group, and between about 5 andabout 30'per cent by volume of a normally liquid dialkyl ether, each ofsaid components having a normal boiling point above about C.

2. A composition according to claim 1 wherein the said aliphaticether-alcohol and the said dialkyl ether components each contains lessthan about 12 carbon atoms.

3. A composition according to claim 1 wherein the said aromatichydrocarbon is toluene, the said aliphatic ether-alcohol is themono-butyl ether of ethylene glycol, and the said dialkyl ether isdi-butyl ether.

4. A solvent for paraffin, waxy sludges and the like of petroleum origincomprising:

, V V Percent by volume Toluene -.Q 60-75 Mono-butyl ether of ethyleneglycol 15-30 Di-butyl ether 5-15 5. The" method of removing paraffin,waxy sludges and the like of petroleum origin from petroleum pipelines,

This 7 and the like equipment which comprises washing said equipmentwith a solvent defined by claim 1.

6. The method of removing paraflin, waxy sludges and the like ofpetroleum origin from petroleum pipelines and like equipment whichcomprises washing said equipment with a solvent defined by claim 1 inthe heated state.

7. The method of cleaning wells which have become clogged with paraflin,waxy sludges and the like of petroleum origin which comprisescirculating a solvent defined by claim 1 through the well.

8. The method of treating an oil-bearing formation which comprisesintroducing into a well penetrating said formation a solvent defined byclaim 1, and thereafter applying gas pressure to said solvent to forceit into the interstices of said formation. 7 V

9. The method of treating an oil-bearing formation which comprisesintroducing into a well penetrating said formation a solvent defined byclaim 1, heating said solvent within the well, and thereafter applyinggas pressure on said solvent to force heated solvent into theinterstices of said formation.

10. The method of treating an oil-bearing formation which comprisesintroducing into a well penetrating said formation a solvent defined byclaim 3, heating said solvent within the well, and thereafter applyinggas pressure on said solvent to force heated solvent into theinterstices of said formation.

11. The method of treating an oil-bearing formation which comprisesintroducing into a well penetrating said formation a solvent defined byclaim 1, applying gas pressure to said solvent to force it into theinterstices of said formation, and thereafter introducing a heatedpetroleum hydrocarbon into the Well under pressure.

12. The process of claim 11 wherein the solvent employed is a solventdefined by claim 3.

13. The process of claim 11 wherein the solvent employed is a solventdefined by claim 4.

14. The method of treating an oil-bearing formation which comprisesintroducing into a well penetrating said formation a solvent mixture asdefined by claim 4, appetroleum hydrocarbon of the diesel fuel rangeinto the interstices of said formation, introducing a heated petroleumhydrocarbon of the Diesel fuel range into the Well, applying gaspressure to said petroleum hydrocarbon to force it into the intersticesof said formation, and allowing the well to stand under pressure forseveral days before withdrawing well fluids therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 47,710Fraser Apr. 25, 1865 1,152,392 Breitung et al. Sept. 7, 1915 2,053,285Grebe Sept. 8, 1936 2,098,535 Charch et al. Nov. 9, 1937 2,135,589Monson Nov. 8, 1938 2,356,254 Lehmann et al. Aug. 22, 1944 2,656,332Sprung Oct. 20. 1953 2,672,450 Pearsall Mar. 16, 1954

1. A SOLVENT FOR PARAFFIN, WAXY SLUDGES AND THE LIKE OF PETROLEUM ORIGINCOMPRISING BETWEEN ABOUT 50 AND ABOUT 85 PER CENT BY VOLUME OF ANORMALLY LIQUID AROMATIC HYDROCARBON, BETWEEN ABOUT 10 AND ABOUT 40 PERCENT BY VOLUME OF A NORMALLY LIQUID ALIPHATIC ETHER-ALCOHOL CONTAININGAT LEAST ONE FREE HYDROXYL GROUP, AND BETWEEN ABOUT 5 AND ABOUT 30 PERCENT BY VOLUME OF A NORMALLY LIQUID DIALKYL ETHER, EACH OF SAIDCOMPONENTS HAVING A NORMAL BOILING POINT ABOVE ABOUT 100* C. 8.A THEMETHOD OF TREATING AN OIL-BEARING FORMATION WHICH COMPRISES INTRODUCINGINTO A WELL PENETRATING SAID FORMATION A SOLVENT DEFINED BY CLAIM 1, ANDTHEREAFTER APPLYING GAS PRESSURE TO SAID SOLVENT TO FORCE IT INTO THEINTERSTICES OF SAID FORMATION.